Alternating current dynamo-electric-machine winding



5 2 9, 1 2 .w u J C. MACMILLAN ALTERNATI NG CURRENT DYNAMO HINE WINDINGELECTRIC MAC Original Filed Aug. 8, 1924 MacmiHam,

In ntor pb His Attofjey.

RM July 21,- 1925.

1 UNITED STATES- Re.'16,l2l PATENT oFFICE.

or SCHENECTADY, new yoamassmxon r enunnar. nnnc'rarc column, Aconrona'rrou or NEW YORK.

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Original Ho. 1,580,466,1dated Harsh 17, 1925, Serial No. 730,968, filedAugust 8, 1924. Application i Y v reissue filed Kay 22, 1925. Serial No.82,205.

To all whom ithdflihoncehh Be it known that'g I, Cmranm. MAcMiL- LAN acitizen of the United- States, residing at ,chenectad in the county ofSchenectady, State of ew;York, have invented certain new and usefulImprovements in Alter- ,natin I Current Dynamo- Electric-Machine Winfication. I

My invention. relates to the windings of of which thefollowing is aspeci- 'alternating current dynamo electric machines and its ob'ect.isto provide a simple and efiicientwin in arrangement which is omdetrimental harmonies. Such a winding has a special value as'a windingfor induction motors.

In selecting primary induction motor windings." for use in conjunctionwith squirrel cage secondaries, it is necessary to take certainprecautions against the production of higher harmonics offlux. andcurrent which might prove detrimental in operation. The objectionaloperatin features to lieguarded against 'arechie y: inductionsubsynchronou's and synchronous subsynchronous speeds commonly. calledcrawling s eds'and locking at' standstill. These decots are caused byhigher harmonics of primarycurrent distribution, of permeance variationsin the air gap, or by combinations of the two in certain relationships.

The harmonics of primary current distribution, or winding harmonics, maybe care in the selection of approriate coi pitches in conjunction withthe istribution constants whlch is determined by the number of phasesand type of winding used. The permeance harmonics must be taken care of-by..a judicious selection of slot numbers, rimary and secondary. In thesuccessful esign of an induction motor other factors mustvalsobeconsidered with the problem of eliminating harmful harmonies. Thus, itis desirable that the winding space he completely and eflicientlyutilized,and that the end connections be simple and not require anexcessiveamount of 00p per. From a manufacturin stand int, it isdesirable that thecoils similar and easily replaced..' Thepresentfinvention'relates to a double layer winding-in which theabove-mentioned factors, going to make up a, successful design, areconsidered together for representation of how a. detrimental windingharmonic is reduced to a harmless value by such a winding arrangement.

Referring to Fig. 1, I have here represented a two layer primary statorwinding for a two pole, three phasemotor having 36 slots with two coilsides per slot, one above the other. Thethree phases are represented by.distinguishing lines. Thus, phase A is represented by light full lines,phase B bvlheavy full lines and phase C by broken lines. It will benoticed that the coils are all similar and, hence, desirable fromamanufacturing standpoint.

Hitherto it has been universally assumed that the best results from thepoint of View of current distribution for any specified 7 number ofphases and slots per pole would always be obtained by-placilig all coilsof one phase per poleiii'i'n adjacent slots. The truth of thisassumption is evident when only the fundamental distribution of currentis considered,="but when harmonics are taken into: consideration it maybe more rofitable to make a slight sacrifice in the ighest value offundamental distribution factor, in order to reduce thedistributionfactors of harmonics, and I have discovered that such aresult can be obtained in certain cases by interchanging the positionsof marginal coils in adjacent phase belts without appreciably affectingthe fundamental line connections to the phases, A, B, and C,

respectively. The connections between coils of a phase belt constitutethe short connecductors in series.

' it will be seen that it has the followin AAAAAABBBBBBCCCCCC. Thefirst- -mentioned arrangement having -marginal coils in adjacent phasebelts interchanged is what I term an interspersed COll winding. By meansof the usual vector polygon representation of distribution constants itcan be shown that the particular interspersed coil arrangement shown ishighly advantageous from. the point of view of suppressing the fifthharmonic without seriously affecting the fundamental distribution.

The vector polygon representation for this particular case is shown inFig. 2 where it is compared to that obtained by the usual windingarrangement. In the present case, we have six slots per phase beltrepresenting 60 electrical degrees so that the vector voltage per slotmust be combined at angles. of 10 (electrical). The distribution factorfor the usual winding would be represented by the length of the cord 2021 in Fig. 2. By the term distribution factor I mean the ratio of thevector sum to the algebraic sum of the voltages contributed by adjacentc'on- Expressed algebraically, this is for the usual winding 2,

2 cos 5+2 cos 15 +2 cos 25 2 cos 5+2 cos 15+2 cos 35 6 which is onlyslightly less than that for the normal win ing.

Considering, now, "the fifth harmonic, the

slot intervals correspond to. 50 electrical degrees, that is to say, thevoltage vectors for the fifth harmonic should be drawn, at

50 to each other so that the fifth harmonic distribution vector diagramper phase belt for the normal winding would be represented by the openpolygon 26, 27, 28 in Fig.

2, and the distribution factor b the length of cord 2628. Expressed agebraically,

this is: I

2 cos 25 +2 cos 75+2 cos 125 6 In most cases this fifth harmonic wouldbe harmful and cause the mot-or tostick at a subsynchronous speed.

For the interspersed winding, the fifth harmonic voltage vector in theoutside slots of the phase belt must be drawn at an angle of 100 insteadof 50 to the next adjacent voltage vectors of the phase belt because ofthe intervening slot so that the vector diagram now becomes 29-31-273330and the distribution factor equal to the len th of cord 2930. Expressedalgebraica ly, this is 2 cos 252 cos 752 cos 175 6 Comparing thesevalues, it is seen that the fundamental distribution factor has beenreduced by 3% by interspersing the coils while the fifth harmonic hasbeen reduced by 71%. The fifth harmonic is thus reduced to a value whenit renders the crawling speed tendency negligible and harmless while thefundamental distribution is not appreciably decreased.

The same process of reasoning applies equally well to the other layer ofthe double layer winding shown in Fig. 1 and the superposition of thetwo layers detracts nothing from the relative immunity of each layerfrom harmonics. 7 Since a double layer winding is specified it issubject to changes in coil pitch without disturbing the interspersing inthe separate layers. Thus, a coil pitch may be selected which rendersthe machine relatively immune from one detrimental harmonic, forexample, the seventh harmonic in accordance with standard practics, andthen the coils may be interspersed to render the winding relativelyimmune fromanother detrimental harmonic, for example, the fifth harmonicin accordance with the present invention.

In the most usual cases, the. number of slots may be such as to provideno opportunity for the complete elimination of one or two harmonics byreduced pitch and interspersing, but each method may secure asubstantial compromise reduction in both harmonics, and the effect ofboth methods, used jointly, is to multiply together the reductionfactors obtained by each method pitch value of the 5th harmonics to 95%and of the 7th harmonics to 27%. Interspersing, which in this casecorresponds in -l25 separately. For example, in the case cited, a coilof 61% pitch only reduces the full.

cficct to a coil pitch reduction in each layer to 83%, reduces the fullpitch values of the harmonics to and 19% respectively. The combinedresult is a reduction of the 5th harmonics to 95x15 1425, and, of the7th to 27x/.19 0514 of full pitch values. This may be accomplishedwithout appreciably lowering the efiiciency of the machine as regardsnormal operation. Thus, in Fig. 1, it is seen that the periphery ofthe-stator is completely utilized with no idle coils or slots, whilesimilar form wound coils may be used without complicated or lengthy endconnections.

harmful harmonic or not.

It is notalways easy to anticipate whether a particular machine will besubject to a The present invention afi'ords an easy way of changingconnections after a machine has come to test and found to have a harmfulharmonic so as to reduce such harmonic to a harmless value. Thus,suppose the machine having the same ole number, pitch, etc. asrepresented in ig. 1, but having the coils connected in the usual waywithout. interspersing, comes to test, and is found to have a harmfulfifth harmonic.

It is only necessary to change the end connections of a few coils torender the machine immune to this harmful, harmonic. This is done bymerely changing shorter end connections like 14 to the longer endconnections like .15, so as to change the connection of the coils inadjacent slots in series at the extremities of each phase belt to theinterspersed arrangement illustrated.

While I have hereinbefore especially mentionedalternating currentmotors, the invention is applicable to any alternating current dynamoelectric machine having a distributed double layer winding where it isdesired to eliminate or reduce detrimental harmonies for any reason. Inaccordance with-the provisions-of the patent statutes, I havedescribedthe principle of'operation of my invention, together with the apparatuswhich I now consider to represent the best embodiment thereof; but

I desire to have it understood that the apparatus shown and described isonly illustrai tive and that the invention rnay be carried outby other.arrangements. What I claim as newxandidesire to secure by Letters Patentof the United States is 1. A harmonic reducing winding arrangement foralternating current dynamo electric machines comprising a slottedmagnetic member having a distributed double. layer alternating currentwinding therein, said winding being made up of similar coils withmarginal coils in adjacent phase beltsinterchanged.

2. A harmonic reducing winding arrangement for alternating currentdynamo electric machines comprising a slotted magnetic member having adistributed. double layer alternating current winding therein, saidWinding having a coil pitch selected so as to make the windingsubstantially immunefrom a particular Winding harmonic and havingmarginal coils in adjacent phase belts interchanged to reduce theharmful effects of another winding harmonic.

3. A harmonic reducing winding arrangement for alternating currentdynamo elec- .trical machines comprising a slotted magnetic member, adistributed double layer alternating current winding in said slots, saidwinding being made up of similar coils and having marginalcoils of theadjacent phase belts interchanged in both layers.

4. A primary member for induction motors comprising a slotted magneticmember having a distributed double layer alternating current windingtherein, said winding being made up of similar coils with marginal coilsin adjacent phase belts interchanged.

5. A primary member for induction motors comprising a slotted magneticmember having a distributed double layer alternat-- ing current windingtherein, said winding having a coil pitch selected so as to makethewinding substantially immune from a particular winding harmonic andhaving mar ginal coils in adjacent phase belts interchanged to reducethe harmful effects of another winding harmonic.

6. A primary member for'induction motors comprising a slotted magneticmember,

a distributed doublelayer alternating cur- I rent winding in said slots,said winding bemg made up of similar coils and having marginal coils ofadj acent phase belts interhaving a distributed double layer alternatingcurrent winding therein. said winding having a coil pitch selected toreduce harmful harmonics and having marginal coils in adj acent phasebelts of both layers interchanged to obtain a still further reduction insuch harmonics.

In witness whereof, havehereunto set my hand this 12th day of May 1925.

CAMPBELL MACMILLAN.

